A number of procedures and systems are used currently for securing bones. One example is the use of a bone plate being secured to a plurality of bones to prevent generally the relative movement of the bones enabling the bones to fuse or heal. Bone plate systems are placed across the joint or fracture site of bones or site of desired bone fusion. As used herein, the term “bone” is used to designate a bone in its entirety, such as a spinal vertebra, as well as a bone fragment.
A number of considerations are involved in the design and use of bone plate systems. For instance, bone plates are implanted in a living tissue environment during a surgical procedure. It is important that no portion of unsecured, foreign material, such as a component of the bone plate system, may be left in the tissue environment post-procedure. Often being relatively small and including component parts, many current bone plates systems are problematic because they cannot be simply handled or manipulated by a surgeon or technician, and because their small components may be dropped into the open-tissue environment and must then be retrieved.
Current bone plates are difficult to place in the desired location because they do not enable the surgeon the ability to simultaneously view the fusion site with the plate in position before securing the plate. This shortcoming is compounded because the tissue environment is difficult to view and presents limiting access to the seam or fusion site.
In many bone plate system applications, it is relatively difficult to secure tightly the bones relative to one another for fusion. As an example, when spinal vertebrae are secured for fusion, bone graft is placed between the vertebral sections. A bone plate is then secured with screws across the fusion site to secure the vertebrae along the spinal axis. It can be difficult to compress properly the vertebral sections because the surgical procedure is performed while the patient is lying prone under anesthesia. However, such a spinal procedure would benefit from the compressive force of gravity. That is, when the patient is allowed to stand erect, gravity is able to compress the vertebral sections and the graft material to benefit healing. In order to enable this, however, the bone plate must allow a slight compression of, or shortening of the distance between, the securing screws in the direction along the spinal axis.
A problem occasionally encountered in the use of bone plate systems is “backing out” of the screws. Specifically, the bone plate is secured with a plurality of screws driven into bones. Due to stresses upon the bones, the performance of some simple bone plate systems has suffered from the screws loosening from, or backing out of, the bones. The loosening of the screws may result from the screw rotating counter-clockwise so as to unthread itself from the bone, or from the threads created in the bone being stripped or otherwise allowing the screw to recede from the bone. Loosening of the screws from the bone allows the plate to move and undermines the ability of the plate to aid in bone fusion, and may cause injury to surrounding tissues.
Another consideration is that the screws and plates are located commonly in a particular orientation by the surgeon implanting the system. For instance, the central axis of the screw can have a particular angle relative to the plate. A surgeon bases this angle on a number of factors to which the performance of the system owes itself. When one or more screws is permitted to alter its desired orientation relative to the plate, the bones tend not to be sufficiently secured relative to each other to optimize the performance of the bone plate system.
Therefore, it is desirable to have an improved bone plate system that, among other things, addresses the foregoing considerations and shortcomings.